The child with a patent ductus arteriosus usually suffers little or no incapacitation but is subject to certain dangers in later life. The arteriovenous communication between the aortic arch and the pulmonary artery is a definite hazard because of the possibility of (1) aneurysmal dilatation and rupture of the ductus or pulmonary artery, (2) thrombosis of the ductus with embolism, (3) subacute bacterial endocarditis or endarteritis and (4) cardiac decompensation resulting from overwork of the heart. Many persons with a patent ductus arteriosus live a long and useful life, but the chances of supervening bacterial endocarditis or cardiac failure are high. In a group of 92 patients who died of this lesion, Maude Abbott1 found that the average age at which death occurred was 24. The seriousness of the prognosis makes worth while treating these children while they are in relatively good health and before fatal complications develop.